1. Technical Field
The present invention relates to a cooling device employed in an image forming apparatus such as a printer, a copier, or a facsimile machine, and to an image forming apparatus employing the cooling device.
2. Related Art
An image forming apparatus includes various devices, such as an optical writing device, a fixing device, a developing device, and a driving motor to rotate an image carrier, each of which generates heat. It is known that these included devices increase the temperature inside the image forming apparatus.
Currently, there are many commercially available color image forming apparatuses such as color copiers and color printers available in the marketplace in response to consumer demand. Such color image forming apparatuses are divided into two types: a single-drum type including a single photoreceptor drum as a latent image carrier, and a tandem type including a plurality of photoreceptor drums. The single-drum type image forming apparatus includes a plurality of developing devices disposed around one photoreceptor drum, in which the developing devices are configured to adhere toner onto the photoreceptor drum in a superimposed manner so that a synthesized toner image is formed thereon and the toner image is then transferred to a sheet of paper, thereby recording a color image. The tandem-type image forming apparatus includes a plurality of photoreceptor drums arranged side by side, each including the developing device, in which a monochrome toner image is formed on each photoreceptor and respective monochrome toner images are sequentially transferred onto a sheet of paper, thereby forming a synthesized color image.
Comparing the single-drum type with the tandem type, it can be seen that because the single-drum type includes only one photoreceptor drum, it can reduce cost. However, because multiple image forming operations must be used to form a full-color image with a configuration employing a single photoreceptor, such an apparatus is not suitable for high-speed image formation. The tandem type has a disadvantage in that the apparatus tends to be larger and more expensive, but has an advantage in that it is suitable for high-speed image formation. Accordingly, with the need for the same high productivity for the full-color printer as for the monochrome printer, the tandem type has garnered attention.
FIG. 9 is an explanatory view of a conventional tandem-type image forming apparatus employing a direct transfer method. FIG. 10 is an explanatory view of a conventional tandem-type image forming apparatus employing an indirect transfer method, in which each image forming unit is disposed above the intermediate transfer belt. FIG. 11 is an explanatory view of a conventional tandem-type image forming apparatus employing an intermediate transfer method, in which each image forming unit is disposed below the intermediate transfer belt.
As illustrated in FIG. 9, the tandem-type image forming apparatus may employ a direct transfer method in which a toner image on a photoreceptor 211 of each image forming unit 210 is sequentially transferred to a sheet P conveyed by a sheet conveyance belt 250. Further, as illustrated in FIG. 10, the tandem-type image forming apparatus may employ an indirect transfer method in which a toner image on the photoreceptor 211 of each image forming unit 210 is once transferred sequentially onto an intermediate transfer belt 260, and then the image on the intermediate transfer belt 260 is transferred by a secondary transfer device 270 en bloc to the sheet P. The secondary transfer device 270 as illustrated in FIG. 10 employs a roller method but the secondary transfer may be performed by a transfer conveyance belt method. Further, as illustrated in FIG. 11, the tandem-type image forming apparatus may employ the intermediate transfer belt 260 disposed above the image forming unit 210.
In the tandem-type image forming apparatus employing the indirect transfer method as illustrated in FIG. 10, the interior of the apparatus is packed with structural parts and components and the fixing device 280 is configured to go underneath each image forming unit 210 to realize a compact apparatus size, and therefore, the fixing device 280 tends to be positioned near each image forming unit 210. When the fixing device 280 is disposed near the image forming unit 210, heat from the fixing device 280, which is a heat-generating member, increases the temperature of the image forming unit 210.
The problem of heat rise of each image forming unit being an image forming part has become a common problem for all image forming apparatuses and is not limited to the tandem-type image forming apparatus employing the indirect transfer method due to keen demand for high speed, compact size, and high quality. Given the compact interior layout of an image forming apparatus employing the electrophotographic method, any image forming apparatus employing any method tend to have a greater generated heat amount inside the apparatus due to the demand for higher printing speed, which may cause defects such as toner agglomeration inside each image forming unit.
To cope with the limited interior space of the image forming apparatus, JP-2005-266249-A discloses an air cooling method that cools the very narrow space of the hot conductive member disposed inside the developing device by blowing air on it. However, despite heat accumulation inside the apparatus, toner with a lower melting point has come to be used to achieve higher quality and performance. Thus, it has come to be difficult to sufficiently cool the image forming unit included in an image forming apparatus such as a high-speed color copier by the air cooling method.
JP-2009-30082-A discloses a more effective cooling device using a liquid cooling method in which a heat receiving part, heat radiating part, pump, and a tube connected to each part to circulate a coolant. However, in the cooling device employing the liquid cooling method, the cooling function is damaged if either the liquid leaks or the pump fails. If the cooling function is degraded, toner agglomeration occurs in each of the image forming units as described above. Accordingly, some measure to detect a leak or a pump failure and notify the user that the cooling function is damaged or to terminate the image forming operation is required.
As to the detection of the leakage of the liquid, for example, there may be a method to detect the leakage of the liquid by disposing a sensor to detect the remaining amount of coolant in the circulation path and determine if the leakage of the liquid has occurred or not. Normally, in the cooling device of the liquid cooling method, because the coolant gradually is evaporated from connection parts between each part and piping over time, the difference between the leakage of the liquid and the evaporation due to the elapsed time is difficult to determine only by the change in the remaining amount of the coolant detected by the remaining amount sensor. Thus, leakage is not detected in one case and leakage is detected erroneously in another case.
In addition, many existing pumps do not include a failure sensor and the pump failure cannot be detected.